Just reading a book on fishes (by Alexrod), listen to this:
"It has been observed through experimentation that in clariids and anabantids, even in well aerated water, the gills may not provide enough oxygen to satisfy the requirements of the system, and death may ensue a short a time as half an hour if the fishes are prevented from going to the surface to take gulps of fresh air and expel vivated air"
Interesting, eh?